Scheduler

The scheduler provides the following functionality seamless and parallel to the application execution:

• Reception/transmission of radio telegrams
• Rx and Tx maturity time management
• 1 level repeating
• SmartACK postmaster functionality
• Listen before talk
• Software timer management
• Remote Management

DolphinV4 API implements a unique pre-emptive priority scheduler on the system level. There are two types of tasks:

• single application task
• multiple system tasks

System tasks run pre-emptive to the application task but concurrent to other system tasks, thus a system task can always interrupt the application task. (exception ASynchTask1, read below). System tasks always run to completion and they can't interrupt each other. Exception is the UART ASynchTask that has high priority. This tasks can also pre-empt other system tasks. There is only one application task; thus no parallel application tasks can be executed. The OS implements no message handling. Some system tasks (i.e. Timer1) can execute application code using static callbacks.
tasks are divided into synchronous and asynchronous tasks. Most of the synchronous system tasks provide the function of the radio protocol stack.

Synchronous system tasks
The synchronous system tasks are handled using the scheduler triggered by the Timer0 HW interrupt. The scheduler runs on a round robin basis and every task has an 1 ms timer slice. Every 1 ms the execution of the application is interrupted and one of the synchronous system tasks takes over the CPU. Synchronous system tasks are executed sequentially according to their priority and demand. The average duration of the synchronous task is around 50 - 150 us. In rare worst case scenarios the execution duration can be up to ~1 ms (considering high radio traffic, long radio telegrams, repeater, SmartACK on).

The execution duration is dependent on:

• Active SmartACK Postmaster feature
• Active repeater feature
• The number of radio buffers
• Amount of radio traffic
• Subtelegram length
  

The following table summarizes all the synchronous system tasks. The list is ordered in descending order of the task priority. Some tasks are executed only if an execution condition is fulfilled.

Task	Description	Execution Condition	Approx. Worst case Duration
SynchTask1	System timer increment - increments a 32bit counter representing the system clock counter (used also by the SW Timers)	every 1ms	~20us
SynchTask2	SmartACK postmaster - provides SmartACK mailbox functionality (processes reclaims, etc.)	every 1ms if SmartACK is active	~250us
SynchTask3	Radio buffer update - processes radio buffers, update subtelegram timing. If there is a telegram that has to be transmitted, it is placed to the radio HW buffer and transmission is started.	every 1ms	~720us
SynchTask4	Telegram compressing - processes received subtelegrams. The occupied buffers are proved if the subtelegram already exists. If the subtelegram is new and repeating is enabled the repeater option is proved.	~500us

Asynchronous system tasks
Asynchronous system tasks are HW module dependent and are connected to HW interrupts. They are active only when the corresponding module and functionality is activated.

Task	Description	Approx. Worst case Duration
Prio High ASynchTask1	Uart Rx/Tx interrupt - processes uart byte receiving/transmitting and buffer handling	~50us
ASynchTask2	Radio Rx interrupt - processes incoming subtelegram	~500us
ASynchTask3	Radio Tx interrupt - stops running HW state machine	~930us
ASynchTask4	Timer1 - processes timer1 interrupts and timer1 callbacks	application dependent
ASynchTask5	IO - processes gpio interrupts and io callbacks	application dependent

Note:

The scheduler is activated by calling the isr_timer0Init or isr_timer0_smack_PM_Init function.

There is no minimum time guaranty for the user application running between the scheduler interrupts!